In a nickel-cadmium secondary battery serving as a high output battery, an electrode comprising a substrate having a layer of sintered porous metal with a large surface area is used so as to generate a large current. The substrate having a layer of sintered porous metal is produced by pressing nickel powder onto a perforated steel sheet, that is, a ground plate, which is plated by nickel with a thickness of 60 to 80 .mu.m, or by applying slurry of nickel powder to it and thereafter sintering the same at a temperature of 900 to 1100.degree. C. in an anti-oxidizing atmosphere. In the above-mentioned temperature range, there is generated necking caused by the solid phase diffusion at the contacting portions of nickel powders with each other, and nickel powders are sintered. At the same time bonding is caused at the contacting portions between the perforated steel sheet with a nickel-plated layer and the nickel powders due to the solid phase diffusion of nickel. Thus, the substrate of a secondary battery electrode is produced by bonding the sintered porous nickel layer, which is composed of the nickel powders bonded to each other at the necking portions to form a network themselves and have about 80% of porosity, to the steel sheet or the ground plate.
However, the substrate of a secondary battery electrode of such structure, that the sintered porous metal is bonded to the ground metal plate only by the solid phase diffusion, has not enough bonding strength, so that the sintered porous metal often peels off from the ground metal plate when the substrate is rolled up and fixed into a cylindrical battery container. This peeling-off occurs particularly in the center portion of the rolled-up substrate where the roll-up radius is too small, which causes problems as shown in FIG. 1 (a) such that an active material falls off due to the peeling-off of the sintered porous metal from the ground metal plate, or the fallen active material and sintered porous metal crash through the separator, to cause a short circuit.
So far, several measures have been taken to increase the bonding strength of the sintered porous metal to the ground metal plate which constitute a substrate of a secondary battery electrode and to improve the strength of the sintered porous metal. Those are as follows:
1) A layer containing metal fiber is formed near the ground metal plate as a core material in order to increase the strength of the sintered metal (Laid Open Japanese Patent No. Sho 64-24364). PA0 2) A layer added by cobalt or the like is formed near the ground metal plate as a core material in order to enhance the solid phase sintering and increase the strength of the sintered metal (Laid Open Japanese Patent No. Hei 5-174831). PA0 3) A surface of the ground metal plate is roughened by etching in order to increase the contacting area thereof with the sintered metal (Laid Open Japanese Patent No. Hei 4-162360). PA0 4) TD nickel plate is used as the ground metal plate in order to increase the anti-peeling strength of it with yttoria particle contacting nickel particle (Laid Open Japanese Patent No. Sho 61-130405).
However, these improvement skills remain within a solid phase sintering technology, and they cannot drastically increase the bonding strength of the sintered porous metal to the ground metal plate constituting a substrate of a secondary battery electrode.
The object of the present invention is to provide an electrode current collector (a ground plate for a substrate) of a secondary battery electrode and a substrate, and a secondary battery electrode and a secondary battery using the same, having sufficient bonding strength so as not to cause peeling-off of the sintered porous metal from the ground metal plate when the electrode is rolled up and fixed into a cylindrical battery container.